1. Field of the Invention
The present invention relates to a clamp apparatus capable of clamping a workpiece by means of an arm which is rotatable by a predetermined angle in accordance with a driving action of a driving mechanism.
2. Description of the Related Art
A clamp cylinder has conventionally been used in order to clamp a component to be welded of an automobile or the like. Such a clamp cylinder is disclosed, for example, in U.S. Pat. No. 4,458,889.
As shown in FIGS. 14 and 15, in the clamp cylinder disclosed in U.S. Pat. No. 4,458,889, a piston rod 2, which is movable back and forth in accordance with a driving action of a cylinder 1c, is arranged between a pair of divided bodies 1a, 1b. A coupling 3 is connected to a first end of the piston rod 2. A pair of links 5a, 5b and a 20 pair of rollers 6a, 6b are rotatably installed to both sides of the coupling 3 respectively by the aid of a first shaft 4. An arm 8, which is rotatable by a predetermined angle, is connected between the pair of links 5a, 5b by the aid of a second shaft 7.
In this case, the pair of rollers 6a, 6b are provided slidably by the aid of a plurality of needles 9a which are installed to holes. The piston rod 2 is provided displaceably integrally with the rollers 6a, 6b in accordance with a guiding action of the rollers 6a, 6b which are slidable along track grooves 9b formed on the bodies 1a, 1b respectively.
However, in the above conventional clamp cylinder disclosed in U.S. Pat. No. 4,458,889, the clamping force of the arm 8 clamping a workpiece is lowered on account of the rotation angle of the arm 8 since the size, the thickness or the like of the workpiece (not shown) held by the arm 8 varies.
In other words, the rotation angle of the arm 8 is changed on account of an attachment attitude or the like of the clamp cylinder when the workpiece is clamped. As a result, the clamping force of the arm 8 clamping the workpiece is changed (lowered).
It is a general object of the present invention to provide a clamp apparatus which makes it possible to maintain substantially constant clamping force of an arm clamping a workpiece even when a rotation angle of the arm is changed.
The above and other objects, features, and advantages of the present invention will become more apparent from the following description when taken in conjunction with the accompanying drawings in which a preferred embodiment of the present invention is shown by way of illustrative example.